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Without checks on emissions, the impacts may be irreversible, report states

Losses outweigh gains for farmers and the poor, it concludes

Your forecast for the next century: Hotter, drier and hungrier, and the chance to turn down the thermostat is slipping away.

That's the latest conclusion from the United Nations, which urged governments to address the "increasingly clear" threats posed by a warming climate before some options are closed off for good. The latest report from the Intergovernmental Panel on Climate Change concluded that taking steps to reduce the carbon dioxide emissions blamed for rising temperatures could buy more time to adjust to a warmer world.

Cutting emissions now "increases the time available for adaptation to a particular level of climate change," the report states. But it adds, "Delaying mitigation actions may reduce options for climate-resilient pathways in the future."

"In many cases, we are not prepared for the climate-related risks that we already face," Vicente Barros, the co-chaiman of the IPCC working group behind the document, said in a statement accompanying the report. "Investments in better preparation can pay dividends both for the present and for the future."

The summary for policymakers was released Monday morning in Yokohama, Japan. It's the second part of the IPCC's benchmark assessment of climate change, a document released every six years with the input of nearly 1,000 scientists. Without checks on emissions, the impacts of climate change will be more severe, more likely, and possibly irreversible, it concludes.

Photos:Climate change: 10 countries most at risk

Photos:Climate change: 10 countries most at risk

10th most at risk: Ethiopia – A farmer and his children plant a field with bean seeds and fertilizer in southern Ethiopia in 2008, a year after severe floods destroyed most of the food crop. Ethiopia is the country 10th most vulnerable to climate change effects, according to a 2013 report by Maplecroft.

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Photos:Climate change: 10 countries most at risk

9th most at risk: Philippines – Manila, capital of the Philippines, is one of the five cities, all in Asia and all projected to be centers of high economic growth, that face "extreme risk" from climate change impacts, according to the Maplecroft report.

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Photos:Climate change: 10 countries most at risk

8th most at risk: Cambodia – Cambodia is among the Southeast and South Asian countries tipped to face an increased risk of severe flooding because of projected changes in seasonal rainfall.

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Photos:Climate change: 10 countries most at risk

7th most at risk: DR Congo – A fisherman sits in a boat on the shore of Lake Kivu in Goma in August. "There are no big fish because of the gas; we only catch small whitebait," one said of the carbon dioxide and methane that saturate the lake.

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Photos:Climate change: 10 countries most at risk

6th most at risk: Nigeria – Floodwaters course through Odo Ona in Nigeria's Oyo State in 2011. At least 102 people were killed when a dam burst during torrential rain.

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Photos:Climate change: 10 countries most at risk

5th most at risk: South Sudan – Tainted water pours into a containment pond in a Unity field processing facility in what is now South Sudan, where there are concerns about the environmental damage being caused by the oil industry.

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Photos:Climate change: 10 countries most at risk

4th most at risk: Haiti – Residents of Jacmel, Haiti, make their way through floodwaters as Tropical Storm Isaac dumps heavy rains in August 2012. An extreme exposure to climate-related events, combined with poor health care access, weak infrastructure, high levels of poverty and an over-reliance on agriculture have led to the country being categorized as at "extreme" risk.

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3rd most at risk: Sierra Leone – Felled trees lie on the mountainside just outside Freetown. African countries account for 14 of the 20 most at-risk nations.

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Photos:Climate change: 10 countries most at risk

2nd most at risk: Guinea-Bissau – Residents walk past the Parliament in Bissau, capital of Guinea-Bissau. African countries rank as at high risk in the index, partly due to their natural susceptibility to events such as floods, droughts, fires, storms or landslides. But their high ranking is also a product of the vulnerability of the population and the inadequacies of existing infrastructure to adapt to or tackle climate change challenges because of weak economies, governance, education and health care.

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Photos:Climate change: 10 countries most at risk

Most at risk: Bangladesh – Bangladeshis attempt to stay dry above flood waters in the capital, Dhaka. Bangladesh was ranked by Maplecroft the country most vulnerable to climate change, and Dhaka the world's most vulnerable city, due to its exposure to threats such as flooding, storm surge, cyclones and landslides, its susceptible population and weak institutional capacity to address the problem.

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Monday's report underscores "that we have committed to a certain amount of warming," said Kelly Levin, an energy and climate expert at the U.S.-based World Resources Institute.

"Over the next few decades, we are going to lock ourselves into a climate change commitment that is going to paint a very different world, depending on what we choose today," Levin said. "The choices we make today are going to affect the risks we face through the rest of the century."

As a result, "Adaptation is emerging as central area in climate change research," Levin said. But adaptation -- steps such as building sea walls, conserving water and designing cities for warmer climates -- has its limits, she said.

"The report suggests some options are going to be too resource-intensive or too expensive," she said.

An increase in atmospheric carbon dioxide and other emissions have driven average temperatures up by about 0.6 degrees Celsius (1 degree Fahrenheit) since 1950, the IPCC says. The first part of its report, released in September, concluded that even a best-case scenario would result in an increase in global average temperatures of 1.6 C; the worst-case scenario estimates a rise of 3.7 degrees Celsius (6.6 Fahrenheit).

The idea that carbon emissions are changing the Earth's climate is politically controversial, but generally accepted as fact by the overwhelming majority of scientists. And as emissions continue to rise, driving up CO2 concentrations in the atmosphere, the impacts will be more severe, more likely and possibly irreversible, Monday's report states.

The summary of the full document -- which is more than 1,000 pages -- will be the premiere guide for lawmakers. It breaks down the expected impacts by continent and by categories such as marine life, agriculture and flood risks. And by diving into the specifics of the report, policymakers will be able to see what risks their specific locations face, as well as what adaptation and mitigation techniques could prove fruitful.

"The real highlight is how many impacts there are, how widespread they are and how pervasive they are around the world," said Heather McGray, who studies adaptation at WRI.

In most cases, climate change will exacerbate existing problems, such as the availability of fresh water in sub-Saharan Africa. The authors conclude that glaciers will continue to shrink "almost worldwide," affecting water supplies downstream.

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Animals have begun shifting their habitats in response to a warming world, and key crops have been affected already, they wrote. Colder climates may see increases in crop yields from longer growing seasons and milder temperatures, but the negative effects are expected to outweigh the positive, the report states.

"In this report, the finding is the impacts of climate change are already widespread and consequential," McGray said.

The impacts won't be the same for everyone, and as usual, the world's poor are more likely to be hurt.

"Climate-related hazards affect poor people's lives directly through impacts on livelihoods, reductions in crop yields or destruction of homes and indirectly through, for example, increased food prices and food insecurity," the report states. Positive effects on the impoverished "are limited and often indirect."

For those people, the effects "will be catastrophic" unless emissions can be reduced, McGray said.